Barcelona striker Zlatan Ibrahimovic is out of Saturday's potentially crucial clash against leaders Real Madrid, the champions said on their website on Friday.
The Swede, who scored the only goal in November's first "Clasico" of the season against Real at the Nou Camp, has not recovered from the calf muscle problem he picked up last weekend, they added.
Real's Brazilian playmaker Kaka has not recovered from a thigh injury in time for Saturday's game, while Spain pair Xabi Alonso and Sergio Ramos return after one-match suspensions.
Real will need several players working together to stop La Liga top scorer Lionel Messi, Real's Spain defender Raul Albiol said on Friday.
"If you give him space he's very dangerous because he has incredible speed with the ball at his feet," Albiol said on Real's website.
"We'll have to help each other a lot, close down the space and try to take him out of his comfort zone."
Pellegrini does not fear Barca even after Messi's demolition of Arsenal in the Champions League on Tuesday, the Chilean told a news conference on Friday.
"I have never been scared of anything," Pellegrini said. "I consider them a very good team but we are not thinking about past results."
The 34-year-old, whom Guardiola deployed in Barca's victorious King's Cup run last season, was signed in January 2008 and has played 18 matches since then and conceded 18 goals.
Real Valladolid's new coach Javier Clemente takes charge of his first match on Saturday since being appointed to replace the sacked Onesimo Sanchez on Monday with the club in 19th spot in the 20-team top division.
"I found the players fairly motivated and they worked with enthusiasm," Clemente said at a news conference on Thursday ahead of their match at fellow strugglers Tenerife. "We have a squad that can compete."
